Mean Annual Flow Research Articles

Decadal trends and predictive insights into aquatic ecosystem health in the Namhan River, South Korea: Longitudinal analysis of hydro-environmental factors and stream health indices (2008–2022)

The main focus of this study is to explore the complex interactions between aquatic ecosystem health (AEH) and time-varying hydro-environmental factors. We measure AEH in the Namhan River of South Korea using stream health index (SHI) scores for the trophic diatom index (TDI), benthic macroinvertebrate index (BMI), and fish assessment index (FAI) for 2008 to 2022. Key hydro-environmental variables associated with AEH, including their time-lagged responses, are identified. Water quality parameters such as chemical oxygen demand (COD) are significantly and negatively correlated with TDI (r=−0.68), BMI (r=−0.87), and FAI (r=−0.70), highlighting the critical role of water quality in the sensitivities of diatoms, macroinvertebrates, and fish health. The apparent response lag of aquatic ecosystems to hydrological parameters, such as a one-year-lagged correlation of BMI with mean flow (r=0.74) and annual flow anomalies (r=0.73), suggests their potential use as predictors in AEH models. A longitudinal analysis of SHIs over a decade showed consistent changes in AEH from upstream to downstream, with notable trends in the deterioration and improvement of SHIs in different areas. The upstream TDI and BMI deteriorated, while the upstream FAI improved. A multiple-linear-regression–based predictive model demonstrated efficacy in predicting AEH under various hydro-environmental conditions, achieving R2 values up to 0.85 for BMI and also has the potential to simulate the impacts of anticipated climatic and hydrological changes.

Detection of Hydrological Alteration and soil erosion in a conserved tropical sub-humid ecosystem of Ethiopia

Soil erosion poses a significant challenge in the sub-humid Ethiopian highlands, yet research on the long-term effectiveness of soil and water conservation (SWC) practices in this region using pre- and post-conservation approaches remains limited. This study addresses this knowledge gap by evaluating the impact of SWC practices on water balance and soil erosion in the Debre Mawi watershed. The study covers two-period analyses: pre-conservation (2010–2014) and post-conservation (2015–2022) using the Soil and Water Assessment Tool (SWAT) to simulate hydrological water balance. Hydrological changes were assessed with the Indicators of Hydrological Alteration (IHA) software. Spatial and weekly sediment distribution were also computed. Results showed the SWAT effectively simulated stream flow, though sediment yield estimation was less accurate. The data demonstrated a reduction in surface runoff by 18% and a decrease in sediment yield by 75%. Conversely, evapotranspiration and groundwater storage experienced increases of 13% and 34%, respectively. The decrease in runoff and sediment can be attributed to the implementation of SWC structures with infiltration furrows, which are presently filled with sediment. Moreover, the expansion of eucalyptus tree acreage may deplete soil water during dry periods, thereby prolonging the time needed for the soil to become saturated and produce runoff, but the impact has yet to be quantified. The IHA analysis confirmed a decrease in mean annual flow from 0.06 m3/s to 0.02 m3/s, and sediment concentration decreased from 831.2 mg/l to 285 mg/l between the pre-and post-conservation periods. The study detected that soil erosion is higher than the allowable limits recommended for Ethiopia even after implementing SWCPs. Additionally, sediment transport reduced after the first three weeks due to improved ground cover and soil stability, although significant amounts were recorded until the end of the rainy season, primarily from gullies. The study found significant hydrological alterations in flow and sediment dynamics following the implementation of SWC practices, particularly pronounced in the early years post-conservation (2015–2018). However, the effectiveness of SWC practices diminished over time, with conditions beginning to revert to pre-conservation levels after 10 years. This suggests that these techniques (infiltration furrows) may be unsuitable for sub-humid watersheds, or that they require improved design and major maintenance beyond the third year. This study offers valuable insights into the dynamics of SWC interventions, underscoring the importance of integrating agronomic practices with SWC efforts to sustain long-term soil and water conservation in Ethiopia's sub-humid highlands. Future research should explore the hydrological effects of eucalyptus expansion and refine SWC practices suited to these unique conditions.

Non‐Linearity in Mean Annual Peak Flow Scaling With Upstream Basin Area: Insights From Percolation Theory

ABSTRACTUnderstanding how annual peak flow, , relates to upstream basin area, , and their scaling have been one of the challenges in surface hydrology. Although a power‐law scaling relationship (i.e., ) has been widely applied in the literature, it is purely empirical, and due to its empiricism, the interpretation of its exponent, , and its variations from one basin to another is not clear. In the literature, different values of have been reported for various datasets and drainage basins of different areas. Invoking concepts of percolation theory as well as self‐affinity, we derived universal and non‐universal scaling laws to theoretically link to . In the universal scaling, we related the exponent to the fractal dimensionality of percolation, (i.e., ). In the non‐universal scaling, in addition to , the exponent was related to the Hurst exponent, , characterizing the boundaries of the drainage basin (i.e., ). The depends on the dimensionality of the drainage system (e.g., two or three dimensions) and percolation class (e.g., random or invasion percolation). We demonstrated that the theoretical universal and non‐universal bounds were in well agreement with experimental ranges of reported in the literature. More importantly, our theoretical framework revealed that greater values are theoretically expected when basins are more quasi two‐dimensional, while smaller values when basins are mainly quasi three‐dimensional. This is well consistent with the experimental data. We attributed it to the fact that small basins most probably display quasi‐two‐dimensional topography, while large basins quasi‐three‐dimensional topography.

Region-scale decline in streamflow across New South Wales catchments

ABSTRACT Changing climate and its interactions with catchments may result in changes to water resources. This study examines the temporal trends in streamflow across New South Wales, Australia. Across 163 catchments with over 35 years of records up to September 2020, we used Mann-Kendall and Sen’s Slope methods to estimate trends in different flow indicators, including the annual, low and high flows, cease to flow, and the rainfall-–runoff relationship. Nearly all (160) catchments have decreasing trends in annual flow, with 62 of these being statistically significant, indicating an overall drying pattern. Most declines are 10–20% per decade relative to the mean annual flows of individual catchments. Trends in rainfall-–runoff relationship suggest that the flow declines are generally greater than expected with given rainfall, and likely due to region-scale processes such as groundwater and vegetation dynamics. Our finding has important implications for future water security for New South Wales and similar environments, such as planning for future reduction in water resources availability with likely increasing demands.

Stream chemical response is mediated by hydrologic connectivity and fire severity in a Pacific Northwest forest

AbstractLarge‐scale wildfires are becoming increasingly common in the wet forests of the Pacific Northwest (USA), with predicted increases in fire prevalence under future climate scenarios. Wildfires can alter streamflow response to precipitation and mobilize water quality constituents, which pose a risk to aquatic ecosystems and downstream drinking water treatment. Research often focuses on the impacts of high‐severity wildfires, with stream biogeochemical responses to low‐ and mixed‐severity fires often understudied, particularly during seasonal shifts in hydrologic connectivity between hillslopes and streams. We studied the impacts of the 2020 Holiday Farm Fire at the HJ Andrews Experimental Forest where rare pre‐fire stream discharge and chemistry data allowed us to evaluate the influence of mixed‐severity fire on stream water quantity and quality. Our research design focused on two well‐studied watersheds with low and low‐moderate burn severity where we examined long‐term data (pre‐ and post‐fire), and instantaneous grab samples collected during four rain events occurring immediately following wildfire and a prolonged dry summer. We analysed the impact of these rain events, which represent the transition from low‐to‐high hydrologic connectivity of the subsurface to the stream, on stream discharge and chemistry behaviour. Long‐term data revealed total annual flows and mean flows remained fairly consistent post‐fire, while small increases in baseflow were observed in the low‐moderately burned watershed. Stream water concentrations of nitrate, phosphate and sulfate significantly increased following fire, with variance in concentration increasing with fire severity. Our end member mixing models suggested that during rain events, the watershed with low‐moderate severity fire had greater streamflow inputs from soil water and groundwater during times of low connectivity compared to the watershed with low severity fire. Finally, differences in fire severity impacts on concentration‐discharge relationships of biogenic solutes were most expressed under low catchment connectivity conditions. Our study provides insights into post‐wildfire impacts to stream water quality, with the goal of informing future research on stream chemistry responses to low, moderate and mixed severity wildfire.

Soil drainage modulates climate effects to shape seasonal and mean annual water balances across the southeastern United States

AbstractClimatic forcing and landscape properties control catchments' hydrological responses over both seasonal and mean annual timescales. Controls on annual and seasonal water balances are usually studied separately which limits and fragments understanding of catchment behaviour. Establishing process controls on hydrological responses that act across multiple time scales could better unify hydrological theory. Here, we use streamflow and climate data from 56 catchments in the Ozarks and Appalachian regions (US) to test how climate (aridity index) and soil drainage together shape seasonal and mean annual water balances for these humid, snow‐free catchments with little precipitation seasonality. We calibrate a simple conceptual model to observed seasonal streamflow and obtain an effective parameter that summarizes the nonlinearity of drainage of soil moisture to groundwater. Our comparative analysis of catchments in the Ozarks and the Appalachian regions indicates that catchments in the more humid climates have lower streamflow seasonality and higher mean annual flow, irrespective of the nonlinearity of soil drainage. In contrast, in relatively drier climates, more nonlinear soil drainage increases the seasonality of streamflow and reduces mean annual flow. Additional testing across 204 humid catchments with little precipitation seasonality and snowfall in the Southeastern United States further supports our hypothesis that soil drainage nonlinearity significantly modulates seasonal and mean annual water balances. These results reveal how soil drainage nonlinearity provides a process interpretation that connects seasonal and annual water balances and highlights the importance of nonlinearity of soil drainage in hydrological modelling.

Reproduction of grass carp (Ctenopharyngodon idella) in the Maumee River, Ohio: Part 2—Optimal river conditions for egg and larval drift

This study uses a one-dimensional steady-state hydraulic model and the Fluvial Egg Drift Simulator (FluEgg) to model the drift and dispersion of grass carp eggs and larvae in the Maumee River, Ohio, for 180 scenarios representing different combinations of 10 river flows, 6 water temperatures, and 3 spawning locations. The FluEgg simulations were used to quantify in-river suspended hatching rates (the percentage of eggs that hatch within the river and in suspension) and in-river larval retention rates (the percentage of larvae that reach the gas bladder inflation stage within the river after hatching in suspension), and identify which scenarios produce the highest likelihood of recruitment. The simulations indicate that at low flows, in-river suspended hatching and larval retention rates in the Maumee River are limited by the capacity of the flow to keep fertilized eggs in suspension, whereas at high flows, the limiting factor is the distance available for the eggs/larvae to drift in the river. A wide range of scenarios result in eggs hatching within the river, but all larvae drift into Maumee Bay prior to the gas bladder inflation stage when flows exceed the mean annual flow. The simulations were assessed in the context of the hydraulic conditions that trigger spawning and maximize egg fertilization and the nursery habitat requirements for larval grass carp. The results indicate that the Maumee River, although suitable for grass carp spawning, may not be an ideal setting for recruitment unless Maumee Bay provides adequate nursery habitat for larvae.

Flood frequency analysis using mean daily flows vs. instantaneous peak flows

Abstract. In many cases, flood frequency analysis (FFA) needs to be carried out on mean daily flows (MDF) instead of instantaneous peak flows (IPF), which can lead to underestimation of design flows. Typically, correction methods are applied to the MDF data to account for such underestimation. In this study, we first analyse the error distribution of MDF-derived flood quantiles over 648 catchments in Germany. The results show that using MDF instead of IPF data can lead to underestimation of the mean annual peak flow (MHQ) by up to 80 % and mainly depends on the catchment area but appears to be influenced by gauge elevation as well. This relationship is shown to differ for summer vs. winter floods. To correct such underestimation, different linear models based on predictors derived from MDF hydrograph and catchment characteristics are investigated. Apart from the catchment area, a key predictor in these models is the event-based ratio of flood peak to flood volume (p/V ratio) obtained by the MDF data. The p/V models applied to either MDF-derived events or statistics seem to outperform other reference correction methods. Moreover, they require a minimum data input, are easily applied, and are valid for the entire study area. The best results are achieved when the L moments of the MDF maximum annual series are corrected with the proposed model, which reduces the flood quantile errors by up to 60 %. The approach behaves particularly well in smaller catchments (<500 km2), where reference methods fall short. However, the limit of the proposed approach is reached for catchment sizes under 100 km2, where the hydrograph information from the daily series is no longer capable of approximating instantaneous flood dynamics and gauge elevations below 100 m, where the difference between MDF and IPF floods is very small.

Impact of anthropogenic changes and rainfall variability on river discharge in tropical Central Africa

Abstract The objective of this study is to investigate the effects of rainfall variability and anthropogenic changes on river discharge in the Benoue and the Logone river basins over the last seven decades (1950–2018). To achieve this goal, hydrometeorological data from these basins were analyzed using the Pettitt and Mann–Kendall tests. Our results show that negative rupture was observed in the hydrometeorological time series of these basins at the annual time step in 1970–1971. The deficits associated with this rupture are estimated at −7% for rainfall and −28% for river flows. The wet season shows similar developments. However, from the 1990s onward, there has been a significant increase in the mean annual flows of the Benoue River, which coincides with that of the rainfall during the same decade. This increase over the recent decades could also be expected in response to an increase in impervious surface area in the catchment area, which could compensate for the deficit generated by the post-1990s rainfall deficit through an increase in runoff. Since the filling of the Lagdo Dam in 1983, an increase in all ranges of minimum flow, as well as an increase in the variability of extreme flows, has been detected.

Bedrock rivers are steep but not narrow: Hydrological and lithological controls on river geometry across the USA

Bedrock rivers are commonly expected to have steeper and narrower channels than alluvial rivers. However, understanding of bedrock river characteristics has largely been based on small samples of sites in specific climates and upland locations. We provide the first systematic assessment of bedrock and alluvial river channel characteristics for 1274 sites across a broad climatic gradient. We assess whether the width, width-to-depth ratio, and slope of bedrock channels differ from those of alluvial channels and the extent to which these differences are correlated with drainage area, mean annual flow (QMAF), grain size, and lithology. We find that bedrock channels occur at all drainage areas. For the same drainage area, bedrock channels are wider and steeper than alluvial channels. They also have a higher mean annual precipitation and hence QMAF, which likely causes the increased width. After accounting for differences in QMAF, both bedrock and alluvial channels have similar hydraulic scaling. Lithology affects both types of channels in a similar way, with channels on sedimentary lithologies being wider and less steep compared to those on igneous-metamorphic lithologies. Overall, our findings raise new questions about the evolution of bedrock river channels and pave the way for more accurate landscape evolution modeling.

A fish biodiversity protection based approach for assessing environmental flow regime in rivers

Available environmental flow assessment methods are not able to integrate the impacts of flow regime on the fish biodiversity which means improving these methods is necessary. This study proposes a novel approach to assess environmental flow regime in which the fish biodiversity index is simulated in the structure of the environmental flow assessment for protecting the fish biodiversity values in the case study. Due to considerable impact of water quality parameters as well as physical flow parameters, two combined physical flow and water quality indices were considered as the inputs of simulating fish biodiversity index. Adaptive neuro fuzzy inference system (ANFIS) as well as hydraulic simulation were applied to simulate combined indices of physical flow and water quality. Moreover, a multiple linear regression (MLR) model was utilized for simulating the fish biodiversity index. Due to necessity of simulating natural flow regime in the representative river reach, soil and water assessment tool as a known hydrological tool was applied as well. According to evaluation indices of the case study, ANFIS model as well as SWAT and MLR are reliable to assess environmental flow considering the fish biodiversity. The minimum environmental flow in the study area was assessed 40% of mean annual flow in which the difference between fish biodiversity index between the natural flow and environmental flow is less than 10%. However, significant improvement of water quality is a prerequisite before implementing the proposed environmental flow regime. High computational complexities is one of the weaknesses of the proposed method.

Effectiveness of an ecological flow regime to assure successful recruitment of anadromous Coregoninae populations in the Rupert River (northern Quebec, Canada)

AbstractObjectiveAs part of a large‐scale hydroelectric project, the mean annual flow of the Rupert River (northern Quebec, Canada) was reduced by 52% at its mouth in 2009. To protect fish habitat, an ecological flow regime that was modulated according to the biological seasons was implemented downstream from the diversion point. An 8‐year monitoring program, including 2 years before partial diversion, was carried out to verify the effectiveness of this mitigation measure on the total annual abundance of anadromous Coregoninae (Cisco Coregonus artedi and Lake Whitefish C. clupeaformis) larvae, which was used as biological indicator of recruitment success. The monitoring also aimed to determine the effects of flow modification on the timing of the larval drift and the spatial distribution of larvae in a river cross section.MethodsEach year, sampling consisted of installing drift nets during the entire downstream larval migration in a river cross section of the lower Rupert River. Drift nets were systematically placed to ensure representative sampling of the river section.ResultPrior to flow reduction, the estimated total number of larvae varied between 1.8 and 8.6 million. Over the following 6 years, the estimated larval population has remained steady at 3–4 million. Otherwise, larval drift characteristics have not changed since the flow reduction, as (1) the duration of the larval drift is the same as before, about 1 month in May and early June, with a peak period of about 8 days; (2) rise in water temperature in spring is a determining factor in the timing of larval drift; and (3) the larvae drift mainly near the surface of the water.ConclusionThe monitoring results indicate that the ecological flow regime implemented in the Rupert River was adequate to maintain anadromous coregonine populations.

Historical climate impact attribution of changes in river flow and sediment loads at selected gauging stations in the Nile basin

The Nile basin is the second largest basin in Africa and one of the regions experiencing high climatic diversity with variability of precipitation and deteriorating water resources. As climate change is affecting most of the hydroclimatic variables across the world, this study assesses whether historical changes in river flow and sediment loads at selected gauges in the Nile basin can be attributed to climate change. An impact attribution approach is employed by constraining a process-based model with a set of factual and counterfactual climate forcing data for 69 years (1951–2019), from the impact attribution setup of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a). To quantify the role of climate change, we use the non-parametric Mann-Kendall test to identify trends and calculate the differences in long-term mean annual river flow and sediment load simulations between a model setup using factual and counterfactual climate forcing data. Results for selected river stations in the Lake Victoria basin show reasonable evidence of a long-term historical increase in river flows (two stations) and sediment load (one station), largely attributed to changes in climate. In contrast, within the Blue Nile and Main Nile basins, there is a slight decrease of river flows at four selected stations under factual climate, which can be attributed to climate change, but no significant changes in sediment load (one station). These findings show spatial differences in the impacts of climate change on river flows and sediment load in the study area for the historical period.

Analysing and evaluating environmental flows through hydrological methods in the regulated Indus River Basin

AbstractEnvironmental flows (EFs), essential for upholding the ecological integrity of rivers and aquatic habitats, have been disrupted significantly by diverting water for agricultural, industrial and domestic uses. This underscores the imperative of implementing sustainable water resource management to harmonize agricultural and environmental needs. The study was conducted in the Indus River Basin (IRB), a region extensively transformed by human interventions. EFs were determined through various techniques, including the flow duration curve shifting method, flow duration curve analysis, low‐flow indices, the Tennant method, the Smakhtin approach, the Tessmann method and the Pastor method. Analysing the estimated EFs alongside downstream flows unveiled specific timeframes (days, months and seasons) of unmet EF requirements. To safeguard the downstream ecosystems, the following EFs were estimated for the respective locations: 880 m3/s (38% of the mean annual flow [MAF]) for the Indus River at Tarbela Dam, 412 m3/s (48% of the MAF) for the Jhelum at Mangla Dam, 425 m3/s (44% of the MAF) for the Chenab at Marala headworks, 389 m3/s (56% of MAF) for the Ravi at Balloki headworks, 184 m3/s (50% of MAF) for the Sutlej at Sulemanki headworks and 231 m3/s (38% of MAF) below Kotri Barrage. The study revealed that violations of EFs occurred 41%, 43%, 44% and 52% of the time during the study period for the Chenab at Marala headworks, the Ravi at Balloki headworks, the Sutlej at Sulemanki headworks and the Indus River at the Kotri Barrage, respectively. The results highlighted that the Chenab, Ravi and Sutlej rivers are particularly susceptible to vulnerability, as the estimated EFs were not consistently upheld in these rivers. These findings underscore the urgent need to take appropriate measures to ensure EFs are not violated, thus safeguarding the downstream ecosystems.

Predicting Streamflow Duration From Crowd‐Sourced Flow Observations

AbstractStreamflow duration is important for aquatic ecosystems and assigning stream protection status. This study predicts streamflow duration, represented as the fraction of time with flow each year, using a combination of sensor data and crowd‐sourced visual observations for a study area in northern Colorado, USA. We used 11 stream stage sensors and 177 visual monitoring points to examine how frequently streams should be sampled to compute flow fractions accurately. This showed that the number of visual observations needed to compute accurate flow fractions increases with decreasing flow duration. We then developed random forest models to predict mean annual flow fractions using climate, topographic, and land cover predictors and found that snow persistence, summer precipitation, and drainage area were important predictors. Model performance was best when using sites with ≥10 visual observations. Our model predicts that almost all (98%) of streams in the study region are non‐perennial, about 10% more than the amount of non‐perennial streams in the National Hydrography Dataset. Stream type maps are sensitive to the time period of data collection and to thresholds used to represent perennial versus non‐perennial flow. To improve maps of non‐perennial streams, we recommend moving beyond categorical classification of streams to a continuous variable like flow fraction. These efforts can be best supported with frequent observations in time that span streams with a wide range of flow fractions and drainage area attributes.

Streamflow responses to forest and climate change in the boreal Da Hinggan Mountains, Northeastern China

AbstractBoreal forests cover vast stretches of land across all continents and represent a principal source area of clean water in the northern hemisphere. Increasingly, studies are conducted on the impact of changes in boreal forest cover on water yield; however, much remains unknown concerning the effects of forest structure changes on stream discharge over the course of multi‐decadal forest harvest cycles. In this study, we analysed long‐term hydrometeorological and forest dynamics data spanning from 1990 to 2016 from a typical boreal forest watershed in the Da Hinggan Mountains in northern China. Our objective was to quantify how changes in forest age and tree species composition affect mean annual streamflow and flow regimes in the context of a changing climate. To distinguish the effects of forest and climate changes on annual streamflow from one another, we employed a combination of a sensitivity‐based method and a temporal trend analysis. Further, we evaluated the impact of forest changes on flow regimes using four indicators: magnitude, duration, frequency, and variability. The results indicated that mean annual streamflow increased by 55.8 mm, with forest changes contributing +61.4 mm compared to −5.6 mm due to climate change (negative effect). This increase occurred when approximately 20% of mature coniferous forests transitioned to mid‐age broad‐leaved forests, accompanied by a 10% increase in total stock volume during the later period. Finally, the effect of changes in forest structure on flow regime were not significant. Our results underscore that variations in forest structure affect streamflow differently depending on stand age and species proportions. Therefore, dynamic forest structure management can benefit not only carbon sequestration but also water supply capacity in boreal forested watersheds.

Environmental flow assessment, evaluation, and suggestions for dying riverine ecosystem of the transboundary Amudarya River, Central Asia

The Amudarya River (ADR) is the largest source of freshwater in Central Asia providing livelihood to millions of people by extracting water for agriculture. However, the over-exploitation has created some critical environmental issues. For example, almost no water for the delta and the Aral Sea, which was once the 4th largest lake in the world. The present study focused on the assessment of environmental flow requirements (E-flows) in the basin. However, the main challenges in the accomplishment were the unavailability of natural streamflow, which is necessary for E-flow assessment, and sparse and limited hydroclimatic data. A hydrologic model was configured to simulate naturalized streamflow using the meteorological data from the Climate Research Unit. Four hydrological methods (i.e., Tennant, low flow index (7Q10), flow duration curve analysis (Q90, and Q95), and flow duration curve shifting (FDCS)) and all-method mean were applied to estimate E-flows at 34 sites on all tributaries of the ADR. According to FDCS, 7Q10, Q90, and Q95, E-flows should be 46%, 37%, 30%, and 25% of naturalized mean annual flow (NMAF), respectively, and on average, it should be 35% of NMAF, assessed by the all-methods mean. For low-flow (October–March) and high-flow (April–September) months, E-flows were determined to be 20–30% and 40–98% of NMAF, respectively. E-flow evaluation with the current environmental conditions showed very serious concerns because no sites met the environmental flow requirements below Kerki. This study will be guidelines to improve the riverine ecosystem and for future sustainable development in the region.

Different groundwater behaviour in deep karst boreholes: the case of Jadro spring basin (Dinaric karst, Croatia)

The paper analyzes the data of groundwater level (GWL), groundwater temperature (TW), and electrical conductivity (EC) measurements in three deep piezometers (B1, B2, B3) in the Jadro spring basin, taken from October 2010 to December 2021. The variation of these parameters is analyzed at different time scales: annually, monthly, daily (24 hours), and hourly. They are compared with the data of the same parameters measured at the Jadro Spring. The analysis of the maximum observed rise and fall rates of the GWL showed that the piezometers were drilled in very different karst environments. Piezometer B1 is located in a karst matrix where the water flows predominantly in a diffuse laminar (slow-flow) regime. Piezometers B2 and B3 are located in a fault line where numerous large karst underground formations occur and rapid turbulent water flow takes place. The mean annual flows of the Jadro Spring strongly depend on the mean annual GWL-s in each of the piezometers. For much of the year (about 99%), the GWL in all three piezometers is more than 210 m below the ground surface. As the measuring sensors are located near the bottom of the piezometers, the groundwater temperature is almost stagnant. It is always at 12.5 ºC in piezometer B1 and behaves almost identically in piezometer B3. Water temperature is the highest in piezometer B2 and hovers around the average value of 13.5 ºC. At the Jadro Spring, the average water temperature is 12.95 ºC. The electrical conductivity values are the highest in piezometers B2 and B3, with an average of around 0.5 mS/cm. They are lower in piezometer B1, where they range around an average value of 0.465 mS/cm, while at the Jadro Spring, they vary from 0.40 mS/cm to 0.48 mS/cm, with an average value of 0.44 mS/cm. A distinct seasonal pattern in groundwater level behavior is evident across all piezometers. However, no discernible upward or downward trend is observed.

Long-term evolution of meandering channel planforms in response to the mean annual flow and width–depth ratio

A depth-averaged linearized meander evolution model was used to numerically evaluate the spatiotemporal evolution of the meandering channel centerline in the plane at various mean annual flows and width–depth ratios for capturing the overall average trend of the meandering channel planform. This analysis was done to better understand the consistent responses of the river morphology to possible future tectonic and climatic changes. The computational cases included an idealized sine-generated meandering channel with a moderate maximum deflection angle and a typical natural meander for the Jiyun River in China. The study results showed phased development and response characteristics of the meandering channel centerline (to the mean annual flow), along with increases in the specified mean annual width (B)–depth (H) ratio (represented by B/H). First, the spatial meander straightening trend over time weakened during Phase 1 (B/H ≤ 16.5) and gradually changed to a meander developing trend during Phase 2 (16.5 < B/H ≤ 27) with an overall insensitivity to the flow magnitude. Second, starting from the downstream tail during Phase 3 (27 < B/H ≤ 28.9), the symmetric development form along the transverse direction (perpendicular to the mean flow direction) was disrupted, while flow effects were highlighted when the mean annual B/H exceeded 28. Finally, an obvious onset and jump process of the channel sensitivity in response to flow occurred during Phase 4 (28.9 < B/H ≤ 29.5). These event characteristics are very similar to the transition from laminar to turbulent flow in fluid mechanics. This study provides insights for more in-depth exploration of meandering mechanisms and technical support for effective river management.

River Park Assessment: 2D Hydraulic Watercourse Modeling for Nature-based Solutions in Urban Area

Over time, fragmentation of semi-natural habitats in urban areas has become a pressing concern, disrupting ecological processes within cities. The focus on preserving open ecosystems has grown, highlighting the need to enhance resilience in urban riverside areas for effective ecosystem restoration. Comprehensive studies on river valleys, considering both hydrology and ecology, play a crucial role in urban river ecosystem development. Our article explores the potential of protective zones with urban vegetation and watercourses as Nature-based Solution within Krakow's ongoing riverine park system development. The study's cross-sections in the River Park area revealed dominant velocities ranging from 0.67 to 2.0 m s-1for SWQ (mean annual maximum flow) and below 0.67 m s-1for Q1% (1% annual exceedance probability flow). The hydrological analysis accurately captured the natural river bed channels' curvature, providing the basis for a two-dimensional mathematical model to visualize the hydraulic structure of protected sites. Integrating water and greenery management systems in urban areas offers significant potential for adapting to climate change, mitigating extreme weather events. Our research's novelty lies in applying 2D hydraulic modeling, demonstrating how River Parks can serve as climate change mitigation solutions in urban environments.